Intermolecular Carbonyl–olefin Metathesis with Vinyl Ethers Catalyzed by Homogeneous and Solid Acids in Flow

The carbonyl–olefin metathesis reaction has experienced significant advances in the last seven years with new catalysts and reaction protocols. However, most of these procedures involve soluble catalysts for intramolecular reactions in batch. Herein, we show that recoverable, inexpensive, easy to handle, non-toxic, and widely available simple solid acids, such as the aluminosilicate montmorillonite, can catalyze the intermolecular carbonyl–olefin metathesis of aromatic ketones and aldehydes with vinyl ethers in-flow, to give alkenes with complete trans stereoselectivity on multi-gram scale and high yields. Experimental and computational data support a mechanism based on a carbocation-induced Grob fragmentation. These results open the way for the industrial implementation of carbonyl–olefin metathesis over solid catalysts in continuous mode, which is still the origin and main application of the parent alkene–alkene cross-metathesis.     

Impact of Dye‐Protein Interaction and Silver Nanoparticles on Rose Bengal Photophysical Behavior and Protein Photocrosslinking

The role of recombinant Type‐I human collagen in the free form or forming AgNP@collagen on the photophysical and photochemical behavior of rose Bengal was analyzed. The formation of dye aggregates on the protein surface was experimentally observed and corroborated by docking calculations. The formation of such aggregates is believed to change the main oxidative mechanism from Type‐II (singlet oxygen) to Type‐I (free radical) photosensitization. Remarkably, the presence of AgNP in the form of AgNP@collagen altered the dynamics of dye triplet deactivation, effectively preventing the dye degradation and reducing the extent of protein crosslinked. Both crosslinked rHC and AgNP@collagen were able to support fibroblasts proliferation, but only the material containing silver was resistant to S. epidermidis infection.     

Stratification of the Radiation Field Inside a Photobioreactor During Microalgae Growth

Light availability is a main issue in autotrophic growth of photosynthetic microorganisms. The change of the suspended cells concentration and that of their chlorophylls content during microalgal growth alters the optical properties of the aqueous suspension. This brings about changes in the properties of the radiation field inside the reactor. In this work, we have computed the evolution in time of the local volumetric rate of absorption of photons inside a photobioreactor by means of a Monte Carlo simulation algorithm previously developed. From this study, we have computed two operational variables that are useful tools for the analysis, performance comparison, optimization and scaling up of photobioreactors: the average rate of photon absorption and the volumetric distribution function of photons absorption rates. Based on these two variables, it is possible to systematically quantify the degree of stratification of the culture medium, which is a decisive aspect that hampers the reactor efficiency regarding the energy usage for biomass production.     

An efficient coarse-grained approach for the electron transport through large molecular systems under dephasing environment

Dephasing effects in electron transport in molecular systems connected between contacts average out the quantum characteristics of the system, forming a bridge to the classical behavior as the size of the system increases. For the evaluation of the conductance of the molecular systems which have sizes within this boundary domain, it is necessary to include these dephasing effects. These effects can be calculated by using the D’Amato-Pastawski model. However, this method is computationally demanding for large molecular systems since transmission functions for all pairs of atomic orbitals need to be calculated. To overcome this difficulty, we develop an efficient coarse-grained model for the calculation of conductance of molecular junctions including decoherence. By analyzing the relationship between chemical potential and inter-molecular coupling, we find that the chemical potential drops stepwise in the systems with weaker inter-unit coupling. Using this property, an efficient coarse-grained algorithm which can reduce computational costs considerably without losing the accuracy is derived and applied to one-dimensional organic systems as a demonstration. This model can be used for the study of the orientation dependence of conductivity in various phases (amorphous, crystals, and polymers) of large molecular systems such as organic semiconducting materials.     

On idempotents of a class of commutative rings

Abstract

In the present work, a procedure for determining idempotents of a commutative ring having a sequence of ideals with certain properties is presented. As an application of this procedure, idempotent elements of various commutative rings are determined. Several examples are included illustrating the main results.     

Solvent-free synthesis of functionalized pyridine derivatives using Wells-Dawson heteropolyacid as catalyst

Wells-Dawson heteropolyacids (H₆P₂W₁₈O₆₂·24H₂O) were used as catalysts in the Hantzsch-like multicomponent condensation reaction with 3-formylchromones as aldehyde component, a β-ketoester and ammonium acetate, under solvent-free conditions at 80 °C. Although the desired products were obtained, functionalized pyridines were the main reaction product and became the alternative route to dihydropyridine ring formation. Based on the proposed mechanisms for the formation of each of the obtained products, the multicomponent reaction was modified to afford only the functionalized pyridines (60-99%). Our procedure represents a clean alternative for the synthesis of several highly functionalized pyridines.